Agricultural machine and system for revisiting a planted plot, and related method

ABSTRACT

This machine includes a tool (30) actuated by an actuating module (32); a dual-frequency satellite positioning module (40) able to take into account corrections relative to the disruptions affecting the propagation of radio navigation signals emitted by each of the visible radio navigation satellites and that are caused by the ionosphere, so as to determine an absolute position of the machine, and consequently of the tool, which is precise to within a centimeter; and a computer (50) able to compare the instantaneous absolute position of the tool and an absolute position of a current revisiting point, selected from among the revisiting points of a revisiting plan, the computer then being able to command the actuation module.

BACKGROUND OF THE INVENTION Field of the invention

The present invention relates to an agricultural machine for revisitinga planted plot.

Revisiting refers to the performance of an agricultural operation on aparcel that has already been planted.

This may be an operation associated with growing the species alreadyplanted on the parcel. This for example involves passing back betweenthe plants of the species that has already been planted, called firstspecies, to perform hoeing or weeding of the soil, spraying fertilizer,or an operation to harvest plants of the first species.

This may also involve an operation relative to growing a second specieson the already-planted parcel. This for example involves passing backbetween the plants of the first species to perform an operation relatedto growing the plants of the second species, such as sowing seeds of thesecond species, hoeing or weeding the soil, spraying a fertilizer at thebase of the plants of the second species, etc.

This may also be an operation to harvest plants of the second species,without harvesting those of the first species. This type of agriculture,called mixed, where several species are grown at the same time on a sameparcel, is regaining interest because it is very advantageous in termsof reducing the quantity of fertilizer used, saving soil, etc.

Description of the Related Art

Document EP 2,404,492 discloses, for the specific case of a vine, amultifunctional agricultural machine in particular making it possible torevisit vines for a hoeing operation of the soil around the vine-stocks.The hoeing tool of the machine is actuated automatically around thevine-stocks based on a signal generated by a proximity sensor, whichassesses the distance between the tool and the vine-stock.

The fact that the already-farmed species is a vine-stock makes itpossible use a proximity sensor. However, the use of a proximity sensorcan be generalized to all types of plants.

Furthermore, a vine-stock is fairly hardy. It allows an actuating errorof the hoeing tool. This is not the case for a plant, such as corn orwheat, whereof the stems remain fragile, especially in the first monthsof growth, when these plants are in the shoot stage and the revisitingoperation must be done.

Furthermore, document US 2003/0009282 discloses an agricultural machinefor planting seeds that is equipped with satellite positioning means ofthe “real-time kinematic” (RTK) type. Based on the actuating moment ofthe tool making it possible to plant a seed and the instantaneousposition delivered by the positioning means, a computer is able to storethe position of each plant seed, in a database.

Positioning means with RTK satellites require the use of a referencereceiver, on the ground, having a known position. This is determinedduring an initial calibration step of the satellite positioning means.

However, satellite positioning means of the RTK type only make itpossible to determine a position that is precise to within about tencentimeters. Such precision is not sufficient for a revisitingoperation.

Furthermore, satellite positioning means of the RTK type have asignificant time deviation. This deviation is not acceptable in the caseof an agricultural machine intended to perform a revisiting operationafter a period of several weeks or several months. Indeed, any deviationin the positioning of the hoeing tool would lead to working a zone inthe soil with a high risk of destroying the farmed plants locatedtherein.

To use such a positioning means, it is then necessary, during therevisiting, to determine the position of the reference receiver by onceagain performing the calibration step. This step is tedious. It must becarried out by the operator of the agricultural machine, which leads toerrors. Lastly, during revisiting, it is necessary for each positionmeasurement to be corrected for the deviation between the position ofthe reference sensor at the time of planting and the position of thereference receiver at the revisiting time.

There is therefore a need for an improved agricultural machine making itpossible to perform an operation related to revisiting a planted parcelsimply and automatically.

The invention aims to meet this need.

BRIEF SUMMARY OF THE INVENTION

To that end, the invention relates to an agricultural revisiting machineand a method for using said machine according to the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention and its advantages will be better understood upon readingthe following description, provided solely as an illustrative andnon-limiting example and done in reference to the appended drawings, inwhich:

FIG. 1 is a diagrammatic illustration of an agricultural machine;

FIG. 2 is a block diagram of the method implemented by the machine ofFIG. 1; and

FIG. 3 is a diagrammatic illustration of an alternative embodiment.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

An agricultural revisiting machine 10 will be described in reference toFIG. 1.

The machine 10 includes a body 12.

As for any vehicle, a reference XYZ is associated with the geometriccenter C of the body 12: the axis X is a longitudinal axis, orientedtoward the front of the body; the axis Y is a transverse axis, orientingthe body 12 from right to left; and the axis Z is an axis perpendicularto the axes X and Y, oriented upward.

The machine 10 includes wheels 14, coupled to traction propulsion means,such as a motor 16, and braking means, such as brakes 18, and steeringmeans, generally designated by reference 20 in FIG. 1.

The propulsion and steering means are designed to allow a driver tocontrol the movement of the machine 10 along the desired trajectory.

Alternatively, the propulsion and steering means are actuatedautomatically by a piloting module of the machine. The latter is thenfully automated and behaves like a robot, the desired trajectory alongwhich the machine is moved then being a computed trajectory.

The machine 10 includes a tool 30, mounted at the rear of the body 12.

The machine 10 is multifunctional, and the tool 30 is mounted removablyon the body 12.

The tool 30 is chosen based on the revisiting operation to be performed.The tool is chosen from among a hoeing tool, a weeding tool, a rakingtool, a tool for sowing seeds, a tool for transplanting plants, aspraying tool, a harvest tool. The tool 30 is mounted temporarily on thebody 12.

In the embodiment shown diagrammatically in the figures, the chosen tool30 is a tool for hoeing the soil.

The machine 10 includes an actuating module 32 of the tool 30, able toactuate the tool 30 in a predetermined manner. Preferably, the actuatingmodule 32 is able to actuate the tool 30 so that the latter performs acharacteristic operating cycle. For the case of a hoeing tool, theoperating cycle can for example consist, relative to a point ofreference on the ground, of hoeing the soil along a first segment, thenalong a second segment, intersecting the first at 90°.

The movement of the tool during its actuation by the actuating module 32is fully determined. In particular, the position and orientation of thefunctional end 34 of the tool 30 relative to the center C and thereference XYZ of the body 12 are known at each moment of the actuationof the tool, based on the instantaneous position of the point C,delivered by the positioning module, and the instantaneous state of theactuating module 32. This information is stored in the actuating module32.

The machine 10 includes a satellite positioning module 40 able todeliver a position and an absolute orientation of the point C and thereference XYZ of the machine with great precision.

The satellite positioning performance is increased by the module 40taking into account disruptions affecting the propagation of radionavigation signals emitted by the satellites, which are caused by theionosphere.

For example, the module 40 is the precise, absolute and deviation-freesatellite positioning module described in document WO 2008/125458. Thispositioning module implements an algorithm called “PPP with wholeundifferentiated ambiguity resolution”, where “PPP” stands for “PrecisePoint Positioning”.

More specifically, each satellite of the constellation of satellitesbroadcasts a first radio navigation signal on a first frequency and asecond radio navigation signal on a second frequency different from thefirst.

A reference station on the ground, belonging to a network of stations,processes the radio navigation signals coming from one of the visiblesatellites, so as to determine corrections, such as an internal delay ofthe satellite and a whole value of the “wide-lane” ambiguity for thereference station. This processing provides for:

-   -   receiving first and second radio navigation signals;    -   an undifferentiated code measurement and an undifferentiated        phase measurement;    -   computing a raw value of the “wide-lane” phase ambiguity;    -   setting an internal delay of the satellite as well as the whole        value of the “wide-lane” phase ambiguity for the reference        station.

The corrections thus determined are sent to broadcasting means towardthe satellite positioning modules of the end users.

A satellite positioning module then performs the following processing:

-   -   receiving the first and second radio navigation signals from a        visible satellite of the constellation of satellites;    -   performing, for each of the first and second received signals,        an undifferentiated code measurement and an undifferentiated        phase measurement;    -   computing a raw value of the “wide-lane” phase from        undifferentiated code measurements and undifferentiated phase        measurements;

acquiring an internal delay of the satellite and determining a wholevalue of the “wide-lane” ambiguity based on said raw value and saidinternal satellite delay.

Aside from the internal delay of the satellite, other correctionsrelative to the satellite visible by the receiver can be computed by thereference stations, sent to the user module and used by the latter forthe precise, to within a centimeter, and absolute determination of itsinstantaneous position.

The module can acquire the corrections relative to each visiblesatellite from a database, for example accessible via the Internet. Themodule is equipped with a wireless communication means, to establish alink with a base station of a radio communication infrastructureconnected to the Internet.

The module can also acquire the corrections relative to each visiblesatellite by capturing appropriate messages, broadcast by SEAS(Satellite-Based Augmentation System) satellites.

Alternatively and more generally, it is possible to make other“wide-lane” and/or “narrow-lane” combinations to determine thecorrections at the reference stations, for both dual-frequency andtri-frequency receivers, as for example described in patent EP 2,335,085B1.

In any case, the module 40 is a dual-frequency module to be able toreceive the first and second radio navigation signals.

The machine 10 includes a computer 50 including computation means, suchas a processor, and storage means, such as a random-access memory and aread-only memory as well as an input/output interface.

The computer 50 is connected to the positioning module 40, the actuatingmodule 32 of the tool 30, and a monitor 52, for example a touchscreen,including a man/machine interface usable by the driver of the machine10.

The computer 50 in particular stores a revisiting plan of the parcel, aswill be described below in relation to the usage method of the machine10. The revisiting plan includes a plurality of geographical revisitingpoints, around each of which the revisiting operation must be done.

From a revisiting plan, the computer 50 is able to develop, online oroff-line, a journey through the parcel that the machine 10 must followto allow the tool to perform the revisiting operation around each of therevisiting points.

The journey developed by the computer 50 is displayed on the monitor 52placed in the cabin to indicate to the driver of the machine 10 how hemust steer the machine.

As shown in FIG. 2, the method 100 includes a step 110 consisting ofperforming an identification of the parcel to be farmed. During thisstep, the operator measures different parameters that may affect howthis parcel is farmed. Thus, certain parameters, for example the slopeof the parcel, its sunshine throughout the year, the rainfall during theyear, the humidity of the soil at different depths and for differentperiods of the year, the quality of the soil, etc., are measured.

The method 100 continues with a step 120 consisting of determining afarming plan of the parcel. This step is advantageously carried out on apersonal computer, which executes a software program to assist withfarming.

The operator first determines whether he wishes to grow one or morespecies on the parcel in question and the nature of the first andoptionally second species to be grown.

The farming plan is next optimized by determining the shape andorientation of the rows of plants on the parcel, the distance betweenthe rows of plants of the first species, the pitch between the plants ofthe first species along a row, the times of year to perform thedifferent operations related to growing the first species, from sowingthe seeds to the final harvest. This information is stored in thefarming plan.

If the operator chooses to grow two species at the same time on theparcel, the farming plan is optimized by determining similar informationfor the plants of the second species. The optimization of the farmingplan for the first species and that for the second species is donesimultaneously, since the positions of the plants of the first speciesaffect the positions of the plants of the second species, and viceversa.

Then, during a step 130, the seeds of the first species are sown.

Advantageously, the machine 10 is used, but with a tool 30 making itpossible to sow seeds.

A sowing plan is extracted from the farming plan. The sowing plan givesthe geographical points of the parcel where seeds of the first speciesmust be sown.

The sowing plan is loaded in the memory of the computer 50 of themachine 10. The operating parameters of the current tool 30 are alsoloaded in the memory of the computer 50.

The computer 50 determines the journey that the machine 10 must followso that the tool 30 can plant seeds of the first species in each of thepoints of the sowing plan.

This journey is displayed in the cabin so that the driver of the machine10 can steer the machine so as to follow this journey as closely aspossible. At each moment, the satellite positioning module delivers theinstantaneous position of the point C of the machine, and the computer50 determines the deviation between the point of the machine and thejourney to be followed, the driver being invited to steer the machine toreduce this deviation.

The machine 10 moves on the parcel such that the tool follows atrajectory overhanging each point indicated in the sowing plan.

When the positioning module 40 delivers an absolute position which,corrected by the computer 50 for a geometric deviation between thecenter C of the machine 10 and the functional part of the tool 30,corresponds to a point of the sowing plan, the computer 30 emits asignal to the actuating means 32 so that the tool 30 sows a seed. Thatseed is then precisely sown at the point whereof the position isindicated in the sowing plan.

The method continues with a step 140 consisting of revisiting the parcelseveral weeks or months after the sowing step 130 for the first species.The parcel is therefore already planted at that time.

For example, the revisiting operation of the planted parcel consists ofhoeing the soil around the plants of the first species that were sown instep 130.

The farmer mounts a tool 30 on the body 12 of the machine 10 based onthe revisiting operation to be done. Here, a hoeing tool 30 is fixed tothe body 12.

A revisiting plan is extracted from the farming plan.

For the case of an operation consisting of hoeing the soil around plantsof the first species, the revisiting plan corresponds to the sowingplan, i.e., the plan for the parcel on which the absolute positions areshown where each seed of the first species was sown.

The revisiting plan is stored in the computer 50, as are the operatingparameters of the hoeing tool 30.

The computer 50 generates a journey of the machine 10 through theparcel, such that the tool 30 can hoe the soil around each pointindicated in the revisiting plan, while avoiding destroying the plantsof the first species.

The journey generated by the computer 50 is displayed in the cabin sothat the driver follows the computed journey.

The machine 10 is moved through the parcel such that the tool 30successively passes near each of the revisiting points indicated in therevisiting plan.

While the machine 10 travels over the parcel, the positioning module 40delivers the absolute position of the center C and the absoluteorientation of the reference XYZ of the machine 10.

Taking into account a geometric shift between the center C of themachine 10 and the functional part 34 of the tool 30, the computer 50determines the absolute position of the point of the soil overhangingwhich the functional part of the tool is located at the current moment.

Each time the computer 50 determines that the tool 30 is located near arevisiting point, the computer 50 sends an appropriate signal to theactuating means 32.

When this signal is received, the actuating means 32 actuates the tool30 so that it performs an operating cycle around a point of referencethat coincides at that moment with the revisiting point in question.

The tool 30 then hoes a zone of the soil which, in fact, is situatedaround the point where a plant of the first species is planted.

The machine 10 is steered through the parcel to perform the entirerevisiting operation.

Alternatively, the hoeing operation can be conducted by hoeing the soilcontinuously by crossing the passes, each past being done along a linefollowing a set of points where the plants of the first species areplanted as closely as possible.

In still another alternative, the revisiting operation is connected togrowing a second species. For example, the revisiting operation of theplanted parcel consists of sowing seeds of the second species betweenthe plants of the first species having been sown in step 130.

The farmer mounts a tool on the body 12 of the machine 10 suitable forsowing seeds of the second species.

A revisiting plan is extracted from the farming plan.

The revisiting plan corresponds to the geographical points of the parcelwhere the seeds of the second species must be planted.

The revisiting plan is loaded in the computer 30 of the machine 10.

From the revisiting plan, the computer 30 develops a journey through theparcel allowing the sowing tool to overhang each revisiting point,without the machine or the actuation of the tool destroying the plantsof the first species.

While the machine 10 travels over the parcel, the Positioning module 40delivers the absolute position of the center C and the absoluteorientation of the reference XYZ of the machine 10.

Taking into account a geometric shift between the center C of themachine 10 and the functional part of the sowing tool, the computer 50determines the absolute position of the point of the soil overhangingwhich the functional part of the sowing tool is located at the currentmoment.

Each time the computer 50 determines that the sowing tool is overhanginga revisiting point, the computer 50 sends an appropriate signal to theactuating means for the sowing tool.

When this signal is received, the actuating means actuates the sowingtool so that it performs an operating cycle around a point of referencethat coincides at that moment with the revisiting point in question.

The sowing tool plants a seed at a point which, in fact, coincides withthe revisiting point.

A first revisiting operation can be followed by other revisitingoperations. For example, after having sown a second species, anotherrevisiting operation could consist of hoeing the soil around the plantsof the first species and/or the plants of the second species. Anappropriate revisiting plan is extracted from the farming plan, whichincludes, as revisiting point, the points where the seeds of the firstand second species have been sown.

A revisiting operation may also consist of harvesting the plants of thefirst (second, respectively) species without touching those of thesecond (first, respectively) species.

In another embodiment shown in FIG. 3, the agricultural machine 210 ismade up of a tractor 211 and a trailer 212, hitched to the tractor. Thetrailer is for example hitched by means of a ball joint, such that thedifferent parts of the machine 210 are articulated relative to oneanother.

The revisiting tool being supported by the trailer 212, the satellitepositioning module 40 is then implanted on the trailer to obtain ameasurement of the position of the tool at each moment.

However, it is desirable, during the revisiting of the planted parcel,not only for the tool to perform the operation associated with therevisiting, but also for the machine as a whole not to destroy theplants 250 that have already been planted on the parcel through whichthe vehicle must travel.

In a first alternative, only the footprint of the machine 210 isconsidered.

The shape of the footprint of the tractor and that of the trailer arepredetermined. It corresponds to the imprint 260 of the front tires ofthe tractor 211, the imprint 261 of the rear tires of the tractor 211,the imprint 262 of the tires of the trailer 212.

Furthermore, a footprint 251 is associated with each plant 250 that hasalready been planted. For example, a sunflower seed planted at aparticular point P of the parcel is associated with an imprint of theplant, for example corresponding to a disc centered on the point P andhaving a predefined radius.

The journey that the tractor must follow for the tool, supported by thepulled trailer, to pass through the revisiting points of the revisitingplan is determined taking into account the constraint according towhich, at each point of this journey, the footprint of the machine mustnot cover part of the imprint of a plant that has already been planted.

The optimal journey thus computed is next loaded into the memory of thecomputer 50 onboard the machine 210, preferably onboard the tractor 211.Then, the tractor travels through the parcel following the optimaljourney. The tool carried by the pulled trailer is actuated to performthe revisiting operation regularly.

In a second alternative, the steric footprint of the machine isconsidered, i.e., its volume, or at the very least a gauge within whichits volume fits. This gauge includes a part above the soil and a partbelow the soil: the part above the soil corresponds to the gauge of thetractor 270, the gauge of the trailer 271 and the part of the gauge ofthe tool above the soil 273; the part below the soil corresponds to thepart of the gauge of the tool below the soil 272, for example when thetool is actuated and pushes into the soil over a predetermined depth.

The steric footprints of the tractor, the trailer and the tool arepredetermined. Their relative positions during the different possiblemovements of the machine 210 and the actuation of the tool make itpossible to define the steric footprint of the machine.

Furthermore, a steric footprint is associated with each plant 250 thathas already been planted. For example, a sunflower seed planted at aparticular point P of the parcel has an associated imprint for examplecorresponding to the junction of a cylinder 254 for the stem (centeredon the point, having a predefined radius and a predefined height), asphere 256 corresponding to the flower (at an upper part of the stem),and a cone 252 corresponding to the roots of the plant (the apex of thecone coinciding with the lower end of the cylinder of the stem).

The journey that the tractor must follow for the tool, supported by thepulled trailer, to pass through the revisiting points of the revisitingplan is determined taking into account the constraint according towhich, at each point of this journey, the steric footprint of themachine must not interfere with a steric footprint of a plant that hasalready been planted.

The optimal journey thus computed is next loaded in the memory of thecomputer onboard the tractor. Then, the tractor travels through theparcel following the optimal journey. The tool carried by the pulledtrailer actuated to perform the revisiting operation regularly.

In order to verify that the tractor is in fact following the computedoptimal journey, it is necessary to know its position at each moment.

To that end, the tractor may also be equipped with a dual-frequencysatellite positioning module 241 able to take into account correctionsrelative to disruptions affecting the propagation of radio navigationsignals emitted by each of the visible radio navigation satellites andthat are caused by the ionosphere, so as to determine an absolute andprecise position of a characteristic point of the tractor. In this way,it is possible to measure an absolute position of the tractor at alltimes. If this position of the tractor or that of the trailer deviatesfrom the optimal journey to be followed, an appropriate correction isapplied to the means for steering the movement of the tractor. Thepositioning module of the trailer makes it possible to determine themoment at which the tool overhangs a revisiting point, in order tocommand the actuating module of the tool and thus perform thecorresponding revisiting operation.

In one alternative, the instantaneous position of the tractor isdetermined by using a kinematic model of the assembly formed by thetractor and the trailer with its tool. This model makes it possible todetermine the instantaneous position of the tractor, from theinstantaneous position of the trailer and optionally its past positions,delivered by the satellite positioning module with which the trailer isequipped.

In still another alternative, falling between the two previousalternatives, if the trailer is provided with a satellite positioningmodule, the tractor is simply provided with an inertial measurementunit. The latter periodically delivers measurements of the positionand/or speed of the tractor relative to a calibration position and speedof the inertial measurement unit. For example, the calibration is doneat a zero speed and while the trailer is aligned with the tractor. Bycorrecting the position delivered by the satellite positioning module bya predetermined quantity, which corresponds to the vectorial distancebetween the inertial measurement unit and the satellite positioningmodule, the calibration position of the inertial measurement unit can bedetermined.

Thus, as indicated above, it is possible to monitor the movement of thetractor in order to allow the tool to perform the revisiting operationaccording to the revisiting plan, while preventing the machine fromdestroying the plants that have already been planted.

The optimal journey that the machine must follow is computed, on theground, off-line, by an appropriate system, or by the onboard computeron the machine. In the latter case, the estimate of the journey can bedone off-line, for example before starting the revisiting operation, oronline (i.e., in real-time) during the revisiting operation. The lattersolution offers the possibility of taking the actual movements of themachine into account.

1. An agricultural revisiting machine performing a revisiting operationof a planted parcel, comprising: an actuating module; a tool actuated bythe actuating module,; a dual-frequency satellite positioning module,the dual-frequency satellite positioning module taking into accountcorrections relative to disruptions affecting a propagation of radionavigation signals emitted by each visible radio navigation satellite ofa set of visible radio navigation satellites and caused by anionosphere, so as to determine, at each moment, an absolute position ofthe machine, and consequently of the tool, which is precise to within acentimeter; and, an inertial measurement_unit for determination of aposition thereof, the inertial measurement_unit using, as input,measurements done by the satellite positioning module and implementing akinematic model of the agricultural revisiting machine, the inertialmeasurement unit comparing the absolute position of the tool and anabsolute position of a current revisiting point, selected amongrevisiting points of a revisiting plan stored in a storage means of thehe inertial measurement unit, the inertial measurement unit commandingthe actuation module based on a relative distance between the absoluteposition of the tool and the absolute position of the current revisitingpoint, wherein the inertial measurement unit is adapted for therevisiting operation to be performed in a parcel where seeds/plants of afirst species have been sowed/planted earlier and the revisitingoperation comprises one of a post-sowing/planting operation to beperformed on the plants of the first species and a sowing/plantingoperation of seeds/plants of a second species.
 2. The machine accordingto claim 1, wherein the tool is a hoeing tool, said revisiting planincludes a plurality of revisiting points, each revisiting pointcorresponding to a point of the parcel where a plant of the first plantspecies has been planted, and a computer commands the actuating moduleof the tool to hoe a soil around a current revisiting point selected inthe revisiting plan.
 3. The machine according to claim 1, wherein, thefirst plant species having been planted on the parcel, the tool is asowing tool, and each of the revisiting points corresponds to a point ofthe parcel where a seed of the second species must be sown.
 4. Themachine according to claim 1, wherein a computer selects the currentrevisiting point of the revisiting plan based on a journey followed bythe machine through the parcel.
 5. The machine according to claim 1,wherein a computer determines and/or follows a journey allowing amovement of the machine through the parcel such that the tool canperform the revisiting operation for each point of the revisiting plan.6. The machine according to claim 5, wherein the journey is determinedunder a constraint, this constraint consisting of imposing that, at allpoints of the journey, an imprint of the machine does not interfere withan imprint associated with a plant that has already been planted.
 7. Themachine according to claim 6, wherein the imprint of the machine and theimprint associated with a plant that has already been planted are of thefootprint or steric footprint type.
 8. The machine according to claim 1,wherein the satellite positioning module is configured to acquirecorrections broadcast by a network of reference stations.
 9. The machineaccording to claim 8, wherein the satellite positioning moduleimplements a Precise Point Positioning algorithm for processing radionavigation signals of a precise point positioning type withundifferentiated whole ambiguity resolution.
 10. A system comprising:computing means for developing a farming plan for a parcel and toextract a sowing plan and revisiting plan from said farming plan; afirst machine for sowing a seed of the first species according to thesowing plan; and a second machine, according to claim 1, able to performthe revisiting operation for the planted parcel, according to therevisiting plan.
 11. The system according to claim 10, the computingmeans is configured to determine, under a constraint, a journey thatmust be followed by the second machine to perform the revisitingoperation, the constraint consisting of imposing that, at any point ofthe journey, an imprint of the machine does not interfere with animprint associated with a plant that has already been planted.
 12. Anagricultural method for revisiting a parcel planted with a firstspecies, geographical points where plants of the first species wereplanted being known, the method comprising: a step for developing arevisiting plan of the planted parcel, based on an agriculturaloperation to be performed during a revisiting operation and thegeographical points where the plants of the first species were planted,the revisiting plan including a plurality of geographical revisitingpoints; and a revisiting step, using an agricultural machine equippedwith an appropriate tool actuated automatically by an actuating moduleand with a dual-frequency receiver, the machine equipped with one ormore of an inertial measurement units and a computer, the one or more ofthe inertial measurement units and the computer using measurements by asatellite positioning module and implementing a kinematic model of themachine; determining an absolute position of the tool, that is preciseto within a centimeter, by implementing processing of received radionavigation signals, which takes into account corrections relative todisruptions affecting propagation of the radio navigation signalsemitted by a visible radio navigation satellite among a set of visibleradio navigation satellite and caused by an ionosphere, and bycommanding an actuating unit as a function of the absolute position ofthe tool and a current geographical revisiting point, selected in therevisiting plan, wherein the revisiting operation is in a parcel whereseeds/plants of a first species have been sowed/planted earlier andcomprises one of a post-sowing/planting operation to be performed on theplants of the first species or a sowing/planting operation ofseeds/plants of a second species.
 13. The method according to claim 12,wherein, the tool being a hoeing tool, the revisiting points of therevisiting plan correspond to points where plants of the first specieshave been planted, and the revisiting step consists of actuating thetool to hoe soil around each of the revisiting points.
 14. The methodaccording to claim 12, wherein, the tool being a sowing tool, therevisiting points of the revisiting plan correspond to geographicalpoints where seeds of a second species must be sown, and in that therevisiting step consists of sowing seeds of the second species at eachof the revisiting points.
 15. The method according to claim 12,including a step for defining a farming plan for a parcel, a step forplanting the first species according to a sowing plan extracted from thefarming plan, and at least one revisiting step according to a revisitingplan extracted from the farming plan.
 16. The method according to claim12, including a step for determining an optimal revisiting journey thatmust be followed by the machine so that the tool performs a requiredagricultural operation, during which step a constraint is taken intoaccount according to which, at all points of the journey, an imprint ofthe machine must not interfere with an imprint associated with a plantthat has already been planted.